Rhagastis trilineata Matsumura, 1921, Thousand Insects Japan (Additam.) 4: 757. Type locality: "Formosa" [Japan].
Similar to Rhagastis mongoliana but immediately distinguishable by the almost uniform (not distinctly chequered) forewing fringes and the small black discal spot on the hindwing underside. Labial palp segment 2 longer than broad, not narrowed to base. Metanotum with a conspicuous tawny patch at each side.
Japan: 25.v-26.vii (Yakushima); 16.vi-4.ix (Honshu); 23.vii-10.viii (Kyushu).
Larval hostplants. Hydrangea macrophylla (Nozaki & Miyata, 1989).
Japan: Honshu (Nashimoto; Shimohino; Tokyo; Bunkakaikan; Ena; Motosugan; Mikaboyama, 750m; Mt. Kitamuki; Shibata; Bushi; Ohara; Misakubomachi); Shikoku (Dono); Kyushu (Itzukimura; Taku); Yakushima (Aikodake).
The single record from Taiwan appears to be erroneous (Inoue, 1990).
Endemic to Japan.